TIN OXIDE

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: 7440-31-7 (1332-29-2); Chemical Formula: SnO

OSHA formerly had no exposure limit for tin oxide. The ACGIH has an exposure limit of 2 mg/m³ as an 8-hour TWA. The proposed PEL was 2 mg/m³ as an 8-hour TWA PEL; NIOSH (Ex. 8-47, Table N1) concurs, and this limit is established by the final rule. Tin oxide may be a white or yellow-brown powder.

Injection of tin dust intraperitoneally into guinea pigs resulted in a nonspecific, well-vascularized chronic granulomatous reaction (Oyanguren, Haddad, and Maass 1958/Ex. 1-652). Chronic exposure to tin oxide fume and dust results in stannosis, a form of pneumoconiosis. The fume of tin oxide is considered to be a more important source of stannosis than the dust (Dundon and Hughes 1950/Ex. 1-732), but other authorities consider the quality of the dust and the duration of exposure equally important (Robertson and Whittaker 1955/Ex. 1-987). The onset of the symptoms of stannosis may be delayed for years; the appearance of the condition is signaled by difficulty in breathing. One worker who had been exposed to unspecified tin oxide levels for 22 years was tested for stannosis and registered a vital breathing capacity 70 percent of normal and a maximal breathing capacity 61 percent of the predicted value (Spencer and Wycoff 1954/Ex. 1-611).

More than 150 cases of stannosis have been reported in the world literature (Robertson and Whittaker 1955/Ex. 1-987), and five cases were reported in the United States before 1954. No cases of massive fibrosis caused by exposure to tin oxide dust or fume have been reported (ACGIH 1986/Ex. 1-3, p. 574). Only NIOSH commented on tin oxide.

In the final rule, OSHA is establishing an 8-hour TWA of 2 mg/m³ for tin oxide dust and fume. The Agency concludes that this limit will protect workers from the significant risks of reduced pulmonary capacity and stannosis, which are considered material impairments of health, associated with exposure to this substance at the levels permitted by the absence of an OSHA limit.